Drones - Pixhawk

Review & test of Gearbest's Pixhawk and comparison with 3DR's Pixhawk

hugues — Tue, 02 Aug 2016 12:17:06 +0000

Recent 3DR's move not to sell DIY components & parts anymore, pushes hobbyists and prosumers to diversify their supplier's sources. Like many others in the community, my issue is to find an "as good quality as 3DR" alternative for a Pixhawk board. I started looking around for possible 3DR Pixhawk replacement candidates, with a quality I can trust in my builds.

There exist myriads of different "Pixhawk" equivalent boards. Most of them are not direct drop-in replacements as they are equipped with different connectors and have different sizes and shapes. Furthermore, most of them do not share the same quantity and redundancy of sensors (i..e.: two gyro, two accel, compass, baro, etc). A direct drop-in replacement is essential for prosumers and professionals trying to standardize parts, connections and components to a maximum.

Then, I was kindly requested by Gearbest to review some of their new FPV racer quad; offer which I declined being a very poor racer pilot (wouldn't have made justice to their fpv quad), proposing them instead to review their Pixhawk board which looked to be an exact match for 3DR Pixhawk board on all aspects: schematics, size, shape, connectors, etc.

This is what this video is about : a test, review and comparison of Gearbest's Pixhawk (versus 3DR's Pixhawk).

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3DR

Pixhawk

Gearbest

review

test

6S powered Pixhawk 900 mm quadcopter experimenting with 3D printing

hugues — Tue, 02 Aug 2016 11:45:56 +0000

A typical week-end "dronegeek" DIY build project : expermenting with 3D printing to make a 900mm Pixhawk quadcopter, with 380Kv motors, 16" props and powered by 6S batteries.

Click here to watch the video.

Credits for the frame's construction technique : this excellent post from Forrest Frantz on light frame construction techniques

Tags:

3D print

Pixhawk

quadcopter

Package delivered autonomously by AirbotServices' X8 model

hugues — Tue, 28 Jul 2015 17:27:17 +0000

I - Intro

This blog shows an autonomous package delivery with the X8 drone model from AirbotServices.

It further synthesizes hardware, software configuration information to explain how to make a drone delivery, fully autonomous mission based on the opensource Pixhawk autopilot hardware and the APM copter and mission planner software.

Video of Drone package Delivery Mission - AirbotServices X8 - Pixhawk - APM:Copter V3.2.1

II - Delivery mission’s preparation:

II.1 - Safety message:

This video does not intend to promote an illegal nor reckless use of drones. So first thing is ensuring you are in legal order to execute such a delivery mission in accordance to your local regulatory authorities. The mission is here executed fully above privately owned properties with agreement of their owners, in a rural non populated area, keeping permanent line of sight, either from the departure or arrival location (two operators are prepositioned at departure and arrival sites for precaution and take manual control over in case of emergency.

II.2 - Analysis of the delivery mission’s path:

A careful analysis is required of the delivery path the drone will follow in order to: avoid obstacles as we do not have any technologies to detect them yet real time in flight (such as electrical lines for ex), fly around any populated areas to avoid them, take into account the terrain’s topology along the way to avoid hitting hills, mountains, trees,...

To take into account the topography, you have two options in current’s mission planner:

you can plan you waypoints at different altitudes, taking into account the relative altitude differences between waypoints (manual altitude offset management – that is the method that was chosen for this mission as described further);

you could plan your waypoints as usual in mission planner and check the “verify height” checkbox in mission planner’s flight plan window. In this case, the google map ground altitude for each waypoint is added to your waypoint desired altitude. This is theoretically a safer way to go than first method; however we noticed in our tests a few issues: mission planner’s ground altitudes are not the same as google earth altitudes (strange discrepancy) with differences of a few meters (enough to crash!) and google altitudes are incorrect (sometimes also by a few meters);

A future third method will be the best of all, once ready for use: in a next release(s) of APM:Copter, terrain following will be made possible (already available in APM:Plane 3.x). That consists in storing, on Pixhawk’s autopilot microSD card, a terrain database which gives the terrain height in meters above sea level for a grid of geographic locations. Terrain following is different than the current “very height” method as the autopilot will permanently check the topology’s height variations to correct the drone’s altitude (versus the verify height method that only checks the altitude at waypoints, but not between them).

For this current delivery mission, the following manual topology analysis has been done, preferring to calculate and plot the terrain’s height variations manually. The following picture and graph shows the altitude (in meters) of the delivery mission’s path, with departure location (“Home” point) on the left and the arrival location on the right (“delivery target”). The intended delivery mission paths, roundtrip, is a little bit more than 1,5km long (or about 1 mile long for non-MKSA countries):

The picture shows a visual Google Earth representation of the full delivery mission and the ground’s altitude topology along its way.

From such a graph, we now know that:

Home altitude is 265 meters
Target altitude is 298 meters

By difference, an offset of 33 meters must be added to the destination’s waypoints altitudes; further add a safety margin of a few extra meters in order to take into account of :

Pixhawk’s barometer drift issue (that we have discussed already a few times on diydrones) when flying more than a few minutes.
the Google Earth altitude precision errors
your own eventual calculation precision errors!
Total ground travel distance is 765 meters, one way. Be aware that, when flying, your drone will also spend some “travel distances” vertically between waypoints to reach desired altitudes (that has an impact on your batteries/autonomy calculations!)
In this example, there are no higher obstacles above 298 meters. There could be towers, electrical lines, etc…DO NOT FORGET to add a safety margin on your waypoints altitudes to mitigate these eventual obstacles! The only good way to do this is a ground survey at destination. Do NOT RELY solely on Google satellite images as they may date from few years (and in the meantime some pylons, towers and trees may have grown J).

Thus make a thorough terrain reconnaissance, not only at departure and arrival points. Check google map data and complete its imprecisions with a field survey.

III - Hardware & Software configuration:

III.1 – UAV ship hardware selection

For such a delivery mission a reliable ship must be used. It must at least comply with the following requirements:

its lift capacity must exceed with a margin the all-up-weight including payload;
must have an autonomy that exceeds with a margin the total flight’s duration;
must have longest range as possible telemetry for command & control capabilities (+RC transmitter as a backup);
must have redundancy on all critical components for a safe auto mission: redundant motors, two GPS, external compass, etc…

These minimum requirements de facto exclude the use of drone toys or quadcopters. Do not use a drone that is designed for video/pictures applications (such as an IRIS, a Solo, a DJI phantom) to deliver packages: they will not have the required level of safety, nor the capacity to do it.

Being a custom drone builder, AirbotServices chose its X8 model as briefly described in pictures below:

III.2 - Package lock/drop mechanism:

The transported package must be securely fixed to the drone and a release mechanism must be triggered automatically by the autopilot. A good way to do this, limited to packages lighter than one kg, is using Nicadrone’s electro permanent magnet (EPM). A newer EPM version is said to carry heavier payloads but I can’t confirm it. The principle of EPM is a magnet that can be activated and deactivated dynamically by a commanding signal.

The EPM has four mounting screws to be fixed to the drone. A standard PWM servo cable is plugged on one side on the PWM EPM input, and on the other side on one of Pixhawk’s AUX1 (RC9) to AUX4 (RC12) outputs. Actually, for a reason explained further in the trigger mechanism, only RC9 to RC11 can be used with current stable APM:Copter 3.2.1 firmware.

A metal plate such as this,

is fixed to the package. This iron plate matches the magnetized square surface of the EPM device. Although EPM holding strength has been tested by others to maximum 1 Kg of payload, I recommend to mechanically block any “yaw” movement of the metal plate against the EPM magnetized surface; indeed the strength of such magnet is in the vertical Z direction, not in the X or Y directions, where the payload can slip very easily. In this particular case, four little aluminum blockers were glued parallel and against the four metal plate edges. In a way such that any yaw movement of the payload versus the EPM base is avoided.

Furthermore, as a lesson learned the hard way during testing sessions, be careful not to fix the metal plate directly on a metallic package: indeed the magnetization flux is dispersed outside the fixing plate and the overall resulting locking strength is weakened doing so!

Attachment point and vibrations considerations:

A package adds a large surface area to your drone that will as a consequence catch more wind than usual. Furthermore, vibrations of your transport ship will be affected by the added mass and the way it is fixed (how rigid it is) to it.

APM:Copter is sensitive to vibrations and to keep vibrations low is critical for a safe flight as it impacts the compasses, among other things. Without a working compass, a flyaway is guaranteed…In future 3.3 version, vibrations management has been improved but for now, keep them low. It is thus a good idea to dampen and isolate the transported package from the part of your ship’s frame carrying the Pixhawk autopilot. It is even better if you can fix the package to a vibration free zone of your ship you use usually for your cameras.

During testing sessions, it was found that a “hard screw” fixing was the least reliable solution to secure the package and mitigate vibrations; with package losses due to forces exceeding the 1kg holding force of EPM. Reliable results were found with rubber bobbins (secured enough in tensile strength but still offering some elasticity between the payload and the ship’s structure).

On the side of the package fixing point, where the metal plate is fixed, various methods were tried from simple scotch tape to hot glue, etc.. Best method was simply…Velcro. Velcro does not melt under the sun (as would hot glue during a summer delivery mission) and offers some elasticity and vibration isolation.

III.3 – EPM lock/drop control configuration:

The EPM gripper works by sending three different PWM values to its servo input:

a neutral value of 1500 us when the EPM gripper is at rest. This rest state does not consume any power so it is best to leave EPM’s state at neutral when it is not in the action of locking or dropping the payload;
a low value below 1100 us to drop the payload;
a high value above 1800 us to lock the payload.

So the functioning sequence becomes:

to lock the payload : set the PWM signal high for a duration of about one second (the EPM secures best when it is able to cycle a few times its magnet. This takes a bit of time. One second is typically good). Then set the PWM value to neutral.
to drop the payload : set the PWM signal to low for a duration of one second. Then set the PWM signal back to neutral.

According to APM:Copter online documentation EPM PWM signal may bet set via a consecutive pair of DO_SET_SERVO commands. However this did not work in practice as these commands do not allow to maintain the commanded PWM values for a predefined duration (ideally one second). Apparently the default duration of these commands is too short to reliably command the EPM gripper.

Instead, the DO_DIGICAM_CONTROL command is used. This command offers the advantage that it works reliably, reduces the number of commands from two to one and allows to define precisely the PWM signal duration (by tenths of a second). This is how to configure it:

Connect a servo cable between EPM and one of the AUX1 (RC9) to AUX3 (RC11) ports of Pixhawk (AUX4 can’t be used as it is not displayed in mission planner camera trigger dop down list). Lets’ assume RC11 for this example.
Open and connect mission planner to Pixhawk. Go to the initial setup / optional hardware/Camera gimbal menu. Set the shutter option to RC11, set the shutter pushed value to 1900 when you want to lock the payload to EPM; or set it to 1100 when the payload is already fixed to EPM and you’re ready for the drop mission. As shown in pictures below:

Picture above : RC11 configured as the Pixhawk AUX EPM commanding port. Shutter pushed value set to 1900 to lock the payload.

Picture above : Shutter configured to 1100 value (unlock or drop value)

Open then the config/tuning “Extended tuning” window to set the Ch7 option to “Camera trigger”, as shown in image below:

To test the setup is functional,

To test payload lock: follow the steps above by setting the RC11 “pushed” value to 1900; then go in the main flight data screen; hold the payload against EPM; right click on the map to have thr drop down action list displayed and select “Trigger camera now”. You should hear a few clicks from the EPM indicating that the payload is secured.
To test payload drop: same steps as above except the “Pushed” value must be set to 1100. A right click on “Trigger camera now” should release your payload.

IV – Essential APM:Copter parameters to setup:

All parameters are describe in details in various APM:Copter documentation pages. We provide below a list of the critical ones for a delivery mission.

IV.1 – Failsafe parameters:

In a delivery mission it is most probable you’ll loose intermittently or permanently your manual RC control link and your GCS telemetry link. There are different setup choices of failsafe actions in these conditions but the obvious way to go is: “failsafe action and continue with Auto mission”.

In such a delivery mission you probably do not want the ship to land in the middle of the woods once batteries are exhausted. So the first obvious action is to double check your batteries are functioning properly and are fully charged. To verify your batteries are functioning properly and that all LiPo cells look good, we strongly advise to use a battery resistance meter (this check function is integrated in good battery chargers). The measured resistance of all battery cells should be around a few milliOhms and about the same value for all cells. If some cells have a significant higher resistance, do not use these batteries for such delivery missions! (use these batteries for bench tests or less hazardous uses). If a battery is puffed, do not use it!

About the battery failsafe action, you can choose ether for land or return to launch. It is a matter of opinion but I would advise in the context of such a delivery mission to use the return to launch action; it is indeed better to permanently damage your batteries than having your expensive ship landing in the middle of a forested area.

IV.2 – Geofencing:

Do setup the maximum allowed range (i.e. the radius of a circle whose center is the arming location) and altitude in accordance to the delivery mission’s profile. Doing so, check the RTL altitude to make sure it is higher than any obstacle on the mission’s path so that your ship will not return to home through trees…

During test sessions, try a geofence breach to verify it is working as expected. Geofence parameters and breach actions are setup in mission planner / config-tuning tab / Geofence menu.

V – Ground control resources and initial checks before launching the auto mission:

According to the topology of the terrain, the mission length, it might be required to organize more than one ground control team. At least a ground control station must be installed at departure’s location (“Home”). Its job will be to setup, verify and control parameters, ensure the ship is flying correctly in GPS mode before launching the auto mission. It will also ensure the returning ship lands properly.

A second team is organized at target’s destination. This second team will be given means to take over an eventual required manual control of the ship in case of emergency. This manual control can be direct or indirect via the home point’s team.

In this delivery mission, the remote team (at destination) keeps permanent GSM voice contact with the control team @home. Furthermore a video downlink is organized in such a way that both teams keep permanent video monitoring from onboard camera(s).

The ground control team is also responsible to check that the environmental conditions allow for a safe UAV flight. The following site : www.uavforecast.com is an excellent resource for doing so. It provides, per location, information about:

-wind speeds at the altitudes the drone will be flying. For AirbotServices X8 model, a maximum wind speed of 40km/h is fine.

-Kp satellite indicator, giving an indication of the GPS signals quality. It should be under 3.

-Visible sats : higher the better. 8 is a strict minimum. With a M8N, such as the one used on AirbotServices’s X8 model, a fix with more > 12 sats is the norm. It provides an HDOP around 1 ! (2 is the maximum for HDOP for flying an auto mission)

-Temps

-Cloud cover & eventual rain. You should not fly under rain and heavy cloud cover as this may produce important GPS glitches (and eventual material damages on your electronics if not at least IP67 compliant or above).

VI - Pre-flight/initial flight checks considerations:

The RC transmitter is used to launch the mission, by first taking-off in stabilize mode. This is indeed the only way to verify and “feel” that the ship behaves as it should. If during the short stabilize mode checkup, an unusual behavior and/or parameter(s) are noticed, mission should be aborted until problem is identified and fixed. If the stabilize phase passes successfully, the pilot switch for a short moment to “PosHold” mode. The objective is to verify that the GPS and compasses are working fine. If PosHold is not behaving perfectly, abort the mission. And again identify and solve the issues before launching the auto mission.

If Poshold phase has passed successfully, then the pilot may switch the ship to Auto mode, where the delivery mission really begins with the first waypoint, etc.

VII – Mission execution and results:

As shown in the attached youtube video above in this post, the mission was very successful, especially in a surprising target drop location’s precision, under a meter. This might be due to simple luck but certainly partly due to the use of a high precision GPS based on a M8N Drotek model which has an extra-large shield of 8cm x 8cm which is totally compliant to Ublox’s M8 GPS chip ideal antenna configuration.

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Pixhawk flight controller power recommandations

Anonymous — Sun, 15 Jun 2014 22:13:50 +0000

How to Power Pixhawk

Pixhawk should primarily be powered via its power port as shown in this picture,

The power port simultaneously powers Pixhawk and reads voltage and current analog measurements produced by an optional 3DR power module (or other voltage/current measurement devices such as an Attopilot).

To power Pixhawk off the servo rail without a power module, connect a servo or BEC to a power (+) pin and a ground (-) pin of the main outputs. When powering Pixhawk off the servo rail, we recommend adding a Zener diode (part number 1N5339) to condition the power across the rail and prevent it from becoming too high. This method (with Zener diode) can also be used as backup power for Pixhawk when using a power module, so in the case of a failure on the power module, Pixhawk will take power from the output rail. See the voltage ratings below for more information on powering Pixhawk.

Note: The Zener diode should not be used with servos with more than 5V.Digital servos can feed up to 11v into the servo rail when powered off an external 5.1v bec.Pixhawk does not supply power to the servo rail.

Looking for a detailed explanation of power wiring with Pixhawk? Click here for more information about connecting ESCs and servos to Pixhawk.

The following block diagram synthesizes an overview of Pixhawk’s power and ESC wiring,

Diagram acronyms: PDB = Power Distribution Board. PM = pixhawk power port. PM/Atto = optional power module from 3DR or Attopilot alternative for higher than 4S battery voltages.

In this diagram, a 3DR power module (or equivalent device) power Pixhawk through its power port (primary source). One power source is enough but obviously not redundant if the power module fails to power this primary source. Therefore we have represented on the diagram a second backup power source via a 5V BEC that wires to Pixhawk’s output servo rail. If the primary source fails, Pixhawk will automatically switch to this second power source.

Advanced configuration : triple redundant power sources (power module as primary , plus two backup BECs – instead of one- to power Pixhawk’s servo rail):

A simple Tie bus circuit can be used to make the secondary power source redundant ! (therefore the power module can fail, a secondary BEC can fail while the third BEC will take over). In this scheme, a simple MBR1545CT integrated circuit is used. This circuit takes two BEC on its inputs and outputs only of of the two BEC according to the highest voltage (i.e. if BEC1 outputs 5.25V and BEC2 outputs 5.45V, MBR1545CT will pass BEC2 and blocks BEC1).
Here a tie bus circuit wiring diagram and example realisation with the MBR1545CT integrated circuit and a 6 pin JST connector:

A few wiring recommendations:

Always connect a ground reference wire with your ESC’s signal wires on pixhawk servo rail (output ports 1-8). Indeed an ESC’s signal wire should never be left floating without its ground reference (THERE IS NO SETUP WHICH WOULDN’T REQUIRE SIGNAL GROUND TO BE CONNECTED).
It is dangerous to power the Pixhawk only from the servo rail, especially with digital servos. Servos may cause voltage spikes (as shown on illlustration below that shows the servo rail voltage on an oscilloscope when a single digital servo attached to a Pixhawk is moved rapidly ). The key thing is that the digital servo causes the voltage on the rail to rise above the critical 5.7V level. Above that level the Pixhawk power management will cut power to the FMU and the Pixhawk will reboot. If that happens when flying you will lose your aircraft.
It is up to the user to provide a clean source of power for the cases when it is powered off the servo rail. Servos by themselves are not quiet enough.
Do not connect a BEC power source to the RC IN port (black ground, red power and white signal wires from the receiver’s PPM ouput are connected to these RC pins)
Adding an external Zener is a recommendation specifically for systems that are using 5V servos and have the servo rail configured for back up power. Connect the recommended Zener diode with its polarity as indicated on the diagram. Use as short wires as possible or even better, use a standard 3 position JR servo connector with the diode legs directly inserted (and soldered) in the servo female pins. To complement the diode, it is also useful to add a capacitorin parallel to the diode. The capacitor will smooth out eventual voltage ripples. As advised for the diode, the capacitor should be connected with as short wires as possible. Do not oversize the capacitor.

Voltage Ratings
Normal Operation Maximum Ratings
Power module input (4.1V to 5.7V)
Servo rail input (4.1V to 5.7V) UP TO 10V FOR MANUAL OVERRIDE, BUT AUTOPILOT PART WILL BE UNPOWERED ABOVE 5.7V IF POWER MODULE INPUT IS NOT PRESENT
USB power input (4.1V to 5.7V)

Absolute Maximum Ratings
Under these conditions the system will not draw any power (will not be operational), but will remain intact.
Power module input (0V to 20V)
Servo rail input (0V to 20V)
USB power input (0V to 6V)

Tags:

Pixhawk

flight controller

how to power

Training FPV quadcopter

Anonymous — Sun, 15 Jun 2014 17:39:00 +0000

Along gradual building and testing of various UAVs , we accumulate many spare parts that end up laying around. So for a bit of fun we decided to build a trainer quadcopter for FPV fun & training. The attached youtube video shows a FPV kid's initiation journey...

The trainer quad is made of:

-Assembled from various frame parts from : 3DR arms, home made plates, VulcanUAV landing legs, some other frames pieces from HK stuff, etc...

-a Pixhawk autopilot with 3.1.2 fw version

-3DR 880kv motors with 10x4,7 props + quadro ESCs

-powered by a 10.000 mah 4S battery

-5.8Ghz FPV setup with a RMRC 600Tvl camera

-Mobius camera for HD footage

This training quad can be crashed and abused, it is easily fixed.

Video of FPV initiation on a Pixhawk trainer quadcopter

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How-to guide: Pixhawk auto camera trigger (without CHDK)

bendev — Sat, 14 Jun 2014 14:12:42 +0000

How-to guide: Pixhawk auto camera trigger (without CHDK)

1. Introduction:

If you are not using a canon camera, you then do not have access to the CHDK canon firmware which provides advanced automation scripts to automate your camera trigger on your UAV.

There exist on the market other great alternatives for all camera brands (some of them are functionally richer and simpler to use than CHDK). As an example in this guide, I will use the "Stratosnapper V2". This is a little smart thing that allows you to trigger any camera brand (Sony, Canon, Nikon, etc) by many ways : infrared, cable, LANC, etc.

If you'd like more details on this little marvel read here.

I personally prefer the "IR trigger mode" the best because it does not require an extra cable connected to your camera, which is a must when you are using a brushless gimbal. It supposes of course your camera supports an IR trigger function; I thus assume the use of a Sony NEX5 in this guide, widely used for aerial photography among UAV'iers.

Then there is another obstacle for many of us : how does Pixhawk work to trigger such a triggering device in auto mission ? There is a lot of posts on diydrones.com about how to do this with APM, but not much yet on the recent Pixhawk. Therefore this guide will try to document it.

I will end the guide with a practical auto photo taking mission example (making sure it really works!).

2. Parts and hardware connections:

Let's start by a general hardware scheme showing all the required parts and general cabling:

The parts are:

2.1 Pixhawk board

One or more of the 6 AUX ports can be used on Pixhawk (AUX1=RC9, AUX2=RC10, AUX3=RC11, etc.):

In this guide I chose port 2 which corresponds to AUX2 as is illustrated in this detailed view :

By default, only the three first AUX ports can be used (1 to 3, or RC9 to RC11).

To trigger the IR device, we need a servo output (PWM signal), not a relay signal. We will see later what parameters configuration is required in mission planner screens (we can for example also configure 6 AUX ports as PWM outputs ; more details later - let's finish the hw description first).

2.2 IR trigger device

Here an illustration of "stratosnapper" with its inputs/outputs:

You may notice two servo leads are connected on the input side of stratosnapper.

This is one of the most important point in this guide : a servo lead must be used to power the IR device from a BEC (5V in this case); the power provided by the second servo lead coming from Pixhawk AUX2 port DOES NOT provide enough power to make it work !!!

Either you have powered the Pixhawk ouputs rail with a BEC and you are fine, either you must provide a separate BEC power to the IR device. This is also true for any other type of device you will connect on Pixhawk : DOT NOT expect pixhawk to power these devices (and certainly not servos as we already knew in the context of the previous generation flight controller, APM2.x).

Stratosnapper works with a servo lead on one of its 4 servo inputs (yes, you may control stratosnapper from 4 different inputs, isn't that great ?). The servo inputs may be various things : push-button, stick, two way switch, three way switch, etc (all configured by a GUI configuration utility from your PC via usb).

And it ouputs on a IR cable to trigger a IR led that must be placed in front of your camera IR sensor:

2.3 IR Led positionning and camera gimbal

The IR led works perfectly, even under a bright sun (verified on the field); it works even quite faraway from the sensor (no problem 5 inches away of the Sony NEX5 sensor) and works fine in any orientation versus the sensor.

Shown here is a picture of an X8 UAV. The Sony NEX5 is held in a 2-axis stabilized brushless gimbal (NEX5 not shown...).

Here below a zoomed view of the IR LED positionning and gimbal:

Gardeners & farmers are notoriously UAV friendly; use some gardening wire to shape your IR LED cable, so it is correctly positionned in front of the camera's IR sensor.

3. Software and parameters configuration:

3.1 Mission planner:

We need to configure Pixhawk to output a servo command on AUX2 (RC10) to trigger stratosnapper which will in turn trigger the IR LED which will in turn trigger the camera. And this needs to happen automatically during an auto mission.

How do we do this ? By using the CAM_TRIGG_DIST function or by using a programmed DO_DIGICAM_CONTROL command. In this guide we will only document the CAM_TRIGG_DIST function.

The CAM_TRIGG_DIST function will command your UAV to take picture everytime it has moved a certain distance (in meters). This is very useful to take pictures at precise distance intervals during geomapping missions or photogrammetry missions.

To configure CAM_TRIGG_DIST, go in mission planner, click on config/tuning to open the full parameters list. In this list you will find three parameters to configure:

-CAM_TRIGG_DIST : defines in meters the distance between two camera triggers. For an auto mission, leave value at zero. It will be changed automatically during the mission by a DO_SET command, to avoid taking pictures before and after the useful parts of your auto mission.

-CAM_TRIG_TYPE : defines if you want the Pixhawk AUX output used to control a relay or to ouput a PWM signal. In the case of an IR device we need a PWM servo signal, so we set it to a value of zero.

-CH7_OPT: internal firmware parameter. In this case, it does NOT correspond to the CH7 of your receiver. You must set it to a value of 9 to indicate the firmware that it must do a camera trigger to the AUX ouput (which will be defined in the camera gimbal setup screen).

Next, we need to define to which AUX ouput we want this servo/PWM signal produced. To do this, open "Initial setup", then "Optional Hardware", then "Camera Gimbal":

In the shutter drop down list, select which AUX port you'd like to use (RC10 = AUX2 in my example).

Then do not forget to adapt the "pushed" and "not pushed" PWM values that will trigger your IR device (stratosnapper in my example). Tune also the duration to the required button pressure duration to trigger your camera (for a Sony NEX5, I set it to 10 = equivalent of 1 second button pressure).

3.2 IR device configuration (stratosnapper V2):

Every IR device comes with its own configuration method. Stratosnapper comes with an ultra easy GUI interface to define which PWM values will trigger what port. It is explained in this video:

(http://player.vimeo.com/video/67660032)

4. Concrete application : test auto mission, applying all of the above

Finally lets' apply all of the above in a true auto mission on the field,

I configured this test auto mission as an example:

To create this auto mission, we can use a very convenient "SURVEY" function of mission planner. You start by drawing a polygon of the zone you'd like to photograph.

Then you right click on the map to select "Survey(Grid)":

It will then show you a configuration screen that will allow you to define which camera make/model you are using and other rather self explanatory parameters (like how much overlap you want between pictures, lens size, etc). The tool will then automatically define for you which is the best CAM_TRIGG_DIST parameter! :

After clicking on "Accept", you will get automatically a list of waypoints starting with a "DO_SET_CAM_TRIGG_DIST" command that will set the distance in meters between two camera triggers during your mission. It ends with another "DO_SET_CAM_TRIGG_DIST" to set the parameter back to zero (stops the shooting).

DO NOT forget to add at least a waypoint (take -off) before and another waypoint (land or RTL) after the last waypoint.

After this is done, after you have passed through your checklist, after you have got all of the authorizations, etc, -> you are then ready to arm, flick the auto switch and off you go!

The above test auto mission lead to this result below. It is a stiched panorama of about 15 pictures; shown here as a reduced thumbnail image (because the full size image is too large at about 107 Mbytes). Click on image for better resolution:

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How-to guide: Pixhawk with 6S batteries (> 4S)

Anonymous — Fri, 13 Jun 2014 09:46:26 +0000

How-to guide: Pixhawk with 6S batteries (> 4S)

1. Introduction:

Pixhawk 3DR kit is delivered by default with a 4S maximum power module. For those wanting to use 5S or 6S or higher voltage batteries this is a “how-to” guide to use for the Pixhawk board.

For those who would like the same “how-to guide” for APM 2.x , here is link :

http://www.diydrones.com/profiles/blogs/powering-your-apm-drone-or-how-not-to-shutdown-apm-like-the-us

Pixhawk comes standard with three (redundant) ways to power it up:

1-USB : not used to fly obviously; just useful on the ground for connection on a ground station software.

2-The power module port accepting a maximum input voltage of 5.7volts (and will not get destroyed up to 20 Volts input)

3-The RC input pins. Will accept a maximum voltage of 5.7volts also (and is also protected up to 20 Volts)

This guide assumes a use of Pixhawk’s power module port which provides not only a way to power the board but also the pins to measure current and voltage values of the main battery.

This guide assumes a use of a 6S battery in combination with a Attopilot current & Voltage sensor board. This Attopilot “power module” replaces the 3DR 4S limited power module. The Attopilot board comes in three flavors: 45 amps, 90 amps or 180 amps.

The choice of the right Attopilot board (45A, 90A or 180 A) will depend on your motor/props combination: take the Attopilot version that has the smallest amps capacity above your max multicopter current consumption. However we will introduce in this guide a way to use the 90 amps Attopilot board to measure up to 150 amps, still using Pixhawk’s power module port.

2. Attopilot description:

An Attopilot board provides three wire soldering pads to solder : a current measurement wire, a voltage measurement wire and a ground wire. See picture below:

Attopilot 90A support up to 50Volts for a maximum of 90A. However the resistor specifications exceed the 90A limitation which makes it possible to use it for measuring 150 amps (we will take this as a assumed max current as our example for the rest of the explanation).

The datasheet of Attopilot specifies that the Voltage measurement wire outputs an analog voltage of 63,69 milliVolt per Volt. Similarly the current measurement wire outputs an analog voltage of 36,60 milliVolt per Volt.

So for a 6S battery the maximum analog voltage values will be:

-For voltage measurement: [min 0V - max 1.6V]

-For current measurement: [min 0V – max 3,3 V]

3. Pixhawk power port description (pinout):

Reusing the excellent pixhawk infographics published in the wiki, the image shows circled in yellow where the power port is on the pixhawk board.

The power port is a so-called DF13 connector with 6 pins.

The six pins of this connector are assigned in the following order, starting by the red wire on the leftmost pin:

Power Port Pinout Description:

1- Vcc (5V input)
2- Vcc (5V input)
3- I (Battery current measurement analog voltage input)
4- V (Battery voltage measurement analog voltage input)
5- Ground
6- Ground

4. Wiring Case 1 : to measure up to a maximum of 90 amps

The connections between Attopilot and Pixhawk are shown in the illustration below:

We have added an optional BEC in the illustration that would be connected to the Vcc and Ground wires of the power module. It is optional as Pixhawk could alternatively be powered via the RC inputs.

4. Wiring Case 2 : to measure up to a maximum of 150 amps

The connections between Attopilot and Pixhawk will integrate resistors to be able to measure up to 150 amps.

Indeed the ADC of this power port on Pixhawk has a range of 0-3.3V. This means that for the maximum true current of 150 amps, we want the current analog wire of Attopilot to output maximum 3.3Volts (as it is the case in case1 for 90 amps max without additional resistors).

Note : this part has been updated with a resistor scheme simplification (only one resistor to add in parallel rather than the originally classical R1, R2 resistors divider) thanks to a contribution of Bo, a diydrones member who analyzed in depth the Attopilot circuitry.

So we will build a small resistors divider on wire 3 (current measurement) & wire 5 or 6 (Ground) as follows:

The Attopilot current measurement output masks a circuit that contains an existing output resistor called Rl. According to the Attopilot datasheet, the following equation links to measured current I (called MeasuredCurrent in the equation), the output analog voltage for current measurement Vout, and an existing Rs resistor in Attopilot:

What we want is to get Vout = 3,3 when Current =150 amps. To do this we will add a new external resisto (Rx) in parallel with the existing Attopilot Rl resistor, so that the new resulting Rl resistor (called Rl’) must be (knowing that Rs = 0.5Mohm as per Attopilot specs):

Therefore we can calculate the Rx resistor value we need to add in parallel as follows:

So, Rx must be ~ 110kohm to have a Vout at 3.3V when the measured current is 150 amps.

You can choose another max amp output (but I would not advise higher than 150 amps with the 90 amps Attopilot, otherwise use the 180 amps version instead) and calculate the resulting Rx resistor

As a result, when the current is 150amps, Vout will have value of 3.3Volts.

5. Mission planner / parameters configuration in battery monitor screen:

In the battery monitor parameters screen, you can manually select which current and voltage sensor you are using. In the present case, you will select the power module and modify the following parameters to make the mission planner voltage and current display match the real values (measured using a wattmeter for example). The explanation below is an extract from the Arducopter parameters list.

Battery monitoring (BATT_MONITOR)

Controls enabling monitoring of the battery’s voltage and current

Value	Meaning
0	Disabled
3	Voltage Only
4	Voltage and Current

Battery Voltage sensing pin (BATT_VOLT_PIN)

Setting this to 0 ~ 13 will enable battery current sensing on pins A0 ~ A13. For the 3DR power brick on APM2.5 it should be set to 13. On the PX4 it should be set to 100. On the Pixhawk powered from the PM connector it should be set to 2.

Value	Meaning
-1	Disabled
0	A0
1	A1
2	Pixhawk
13	A13
100	PX4

Battery Current sensing pin (BATT_CURR_PIN)

Setting this to 0 ~ 13 will enable battery current sensing on pins A0 ~ A13. For the 3DR power brick on APM2.5 it should be set to 12. On the PX4 it should be set to 101. On the Pixhawk powered from the PM connector it should be set to 3.

Value	Meaning
-1	Disabled
1	A1
2	A2
3	Pixhawk
12	A12
101	PX4

Voltage Multiplier (BATT_VOLT_MULT)

Used to convert the voltage of the voltage sensing pin (BATT_VOLT_PIN) to the actual battery’s voltage (pin_voltage * VOLT_MULT). For the 3DR Power brick on APM2 or Pixhawk, this should be set to 10.1. For the Pixhawk with the 3DR 4in1 ESC this should be 12.02. For the PX4 using the PX4IO power supply this should be set to 1.

This is a parameter to adjust to match the real Voltage value with the displayed mission planner value.

Amps per volt (BATT_AMP_PERVOLT)

Number of amps that a 1V reading on the current sensor corresponds to. On the APM2 or Pixhawk using the 3DR Power brick this should be set to 17. For the Pixhawk with the 3DR 4in1 ESC this should be 17. Units: A/V.

This is a parameter to adjust to match the real Voltage value with the displayed mission planner value.

There you go! I hope this will help you configure your pixhawk with higher than 4S batteries.

Cheers,

Hugues

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